This invention relates to a rope traction device and, more particularly, to an improvement in a rope traction device suitable for use in construction, loading and unloading and conveying machines including moving scaffolds, elevators and craces.
A rope traction device is a type of winding instrument used for construction, loading and unloading and conveying machines and is capable of moving up and down along a rope with the rope wound around its sheave by only one or few windings and without winding the rope around and feeding it from a drum.
An example of a prior art rope traction device used for moving up and down a moving scaffold for performing a work along an exterior wall surface of a building is shown in FIG. 9. This rope traction device includes a frame 1, a drive shaft 2 mounted on the frame 1, a motor (not shown) provided on the outer periphery of the drive shaft 2 through a bearing and a sheave 4 driven by this motor. The rope traction device further includes a traction mechanism 6 for holding a rope 5 wound about this sheave 4 by one winding for preventing the rope 5 from slipping off the sheave 4.
This traction mechanism 6 includes an L-shaped pivoting arm provided in the vicinity of a point at which the rope 5 is disengaged from the sheave 4. A pair of rollers 9, 9 are rotatably mounted at one end of the pivoting arm 8 to press the rope 5 inwardly from a straight tightened state thereof. Another pair of rollers 10, 10 are rotatably mounted on a pivoting arm 11 which is pivotably mounted at the other end of the pivoting arm 8.
There is another type of prior art rope traction device disclosed in Japanese Patent Application Laid-open No. Hei 5-32395. In this rope traction device, as shown in FIG. 10, side plates 13, 13 which come into contact with the side surfaces of a rope 12 are made of leaf spring separately from a sheave main body 11. The two side plates 13, 13 are provided at sides of the sheave main body 11 in such a manner that the interval between the inner surfaces of the side plates is made smaller than the diameter of the rope by a predetermined value and the side plates 13, 13 are fixed to the sheave main body 11 by means of bolts 14 alternately or at opposite positions in the circumferential direction of the sheave.
According to this prior art rope traction device, since the side plates made of leaf springs are secured to the sides of the sheave by means of bolts alternately in the circumferential direciton of the sheave, and the interval between the inner-surfaces of the side plates is made smaller than the diameter of the rope, when the rope is received between the side plates, a portion of one of the side plates which is not secured to the sheave by the bolt but is located on the opposite side of a portion of the other side plate which is secured to the sheave by the bolt is flexed in the opposite direction to the portion of the side plate which is secured to the sheave by the bolt, so that the respective side plates are flexed undulatingly in the circumferential direction. As a result, a component force is produced due to the tension of the rope which component force is directed from the center of the rope to the portion of the side plate which is secured to sheave by the bolt and this increases frictional force acting between the rope and the side plates with the result that the pressing force excerted by the side plates to the rope also increases whereby transmission of power from the sheave to the rope is efficiently performed. In the case where the side plates are secured to the sides the sheave by means of bolts at opposite positions in the circumferential direction, the rope received in the groove formed by the side plates is clamped and deformed so as to reduce its diameter in portions of the side plates which are secured to the sheave at opposite positions by means of the bolts whereas portions of the side plates which are not secured to the sheave are flexed outwardly on both sides and, as a result, a wedging force acts on the portions of the side plates which are secured to the sheave by the bolts due to the tension of the rope. As a result, frictional force acting between the rope and the side plates increases with resulting increase in the pressing force excerted by the sheave to the rope.
In the tract i on mechanism 6 of FIG. 9 in which the rope 5 is pressed against the sheave 4 by the pair of rollers 10, 10 mounted on the pivoting arm 11, bending moment is repeatedly applied to the rope 5 at points of contact with the V-shaped groove of the sheave 4 at two positions at which the rollers 10, 10 tend to slip sideways by force applied in transverse direction by twisting of the rope 5. For these reasons, wear occurs in the rope 5 and the life of the rope 5 thereby is shortened. Besides, change in the diameter of the rope 5 due to wear on the rope 5 and the groove of the sheave 4 causes change in the state of the pivoting arm 8 before pivoting with resulting change and instability in the pressing force obtained by the movement of the rollers 9, 9 by the rope 5, that is, the traction force.
In the rope traction device using the side plates 13 shown in FIG. 10, the flextion of the leaf springs applies stress concentrically at portions where the leaf springs are secured to the side plates, i.e., fixing points by the bolts 14. Therefore, the bolts 14 and the portions of the leaf springs about the openings for inserting the bolts 14 there through must have sufficient strength. The leaf springs constituting the side plates 13 must therefore have thickness corresponding to the strength of the portions about these openings where stress is concentrically applied and thus require a large thickness. This requirement for large thickness of the leaf springs, together with the requirement for mounting of the bolts 14, necessitates increase in the weight of the rope traction device as a whole with resulting difficulty in realizing a small and light-weight rope traction device. Moreover, the large thickness of the leaf springs increases the pressing force of the leaf springs against the rope 12 and this results in shortening of the life of the rope 12. Moreover, the large thickness of the leaf springs reduces the amount of flexion of the leaf springs which in turn reduces the rope holding force of the leaf springs.
In the prior art cope traction device of FIG. 10 in which the leaf springs are secured to the sheave main body 11 by means of the bolts 14, assembling and maintenance of the leaf springs are time-consuming and troublesome and, besides, manufacturing of the leaf springs and forming of the openings for the bolts in the side plates 13 and the sheave main body 11 also increases the manufacturing cost of the rope traction device.
Furthermore, since the side plates 13 are made of the leaf springs and it is extremely difficult to process the surface of the leaf spring by machining, it is extremely difficult to obtain a rope groove having a desired sectional shape such as a tapered groove by the side plates 13.
It is, therefore, an object of the invention to provide a rope traction device capable of prolonging the life of a wire rope with minimum wear caused thereon.
It is another object of the invention to provide a rope traction device capable of achieving a stable traction force.
It is another object of the invention to provide a small and light-weight rope traction device with a simplified structure.
It is another object of the invention to provide a rope traction device in which a rope receiving groove of any desired sectional shape can be designed.